UROTHELIAL DIFFERENTIATION: RATIONALE: The main goal of this proposal is to investigate urothelial differentiation. The rationale of this proposal is that reciprocal cell-cell signaling between bladder epithelium, and stroma is necessary for the maintenance of normal urothelium. We hypothesize that normal homeostatic interactions between the bladder epithelium and the underlying stroma are critical for maintaining normal bladder function. A key aspect of normal bladder development is the differentiation of smooth muscle cells from undifferentiated bladder mesenchyme. Likewise reciprocal interactions between the mesenchyme and subsequently the stroma maintain the urothelial cell phenotype. Simple, normal bladder stroma is necessary for normal urothelial function. Conversely, abnormal epithelial-stromal interactions leads to changes of the urothelial phenotype, atypia or cancer. Smooth muscle differentiation is a gradual process during normal bladder development, and characteristic smooth muscle differentiation markers are expressed in a temporally specific sequence. Likewise, urothelial cell differentiation can be documented by a progressive expression of various cytokeratins and uroplakins. In specific aim #1 we propose that the urothelial phenotype can de-differentiate under the influence of "foreign" stroma. Conversely, in specific aim #2 we propose that epithelial cells under the influence of the appropriate stroma can differentiate into urothelium. Specific aim #3 addresses the contribution of specific growth factors as the mechanism of urothelial proliferation and differentiation. The strategy behind specific aim #3 is to use growth factor knock-out and growth factor receptor knock-out animals as the basis of tissue recombination experiments. The long-term objective of this research is to develop effective strategies for inducing and maintaining urothelial differentiation for urinary tract rehabilitation. Understanding and controlling urothelial differentiation may reduce the complications in patients with intestinal augments. Furthermore, we propose that abnormal epithelial-stroma signaling that occurs when intestinal segments are placed in contact with the bladder may lead to cellular changes such as atypia or even cancer.